Boiler tube shielding wall

ABSTRACT

A shielding or insulating wall of discrete tiles is removably secured in front of the impingement surfaces of boiler tubes in the burner region of the boiler furnace chamber for shielding the lower regions of the boiler tubes against excessive heating in order to force combustion gases to rise into the superheat and reheat regions of the boiler to develop and maintain required higher temperatures in such latter regions, or to protect the boiler tubes from direct impingement of burner flames which tend to generate and accelerate their premature deterioration. The shielding wall of tile is free-floating with the expansion and contraction of the boiler tubes, whose load and temperature variation in the burner region of the furnace area normally results in cracking and decay of a fixed continuous shielding wall material as currently practiced.

United States Patent Graham et a1.

[451 Nov. 26, 1974 BOILER TUBE SHIELDING WALL [76] Inventors: Robert G.Graham, 2433 N. Nine Primary Exammer Kenneth Sprague Mile Rd., Sanford,Mich. 48657; Douglas J. Frame, 3774 Lancaster 57 ABSTRACT Dr., Sterlingl-le1ghts, Mich. 48077 I A shielding or insulating wall of discretetiles lS remov- [22] Flledl 1974 ably secured in front of theimpingement surfaces of [21] APPL No; 444,855 boiler tubes in the burnerregion of the boiler furnace chamber for shielding the lower regions ofthe boiler Related -S- Application Data tubes against excessive heatingin order to force com- [62] Division of Ser. No. 323,872, Jan. 15, 1973.bustion gases to rise into the superheat and reheat regions of theboiler to develop and maintain required [52] US. Cl. 122/6 A, 110/98 Rhigher temperatures in such latter regions, or to pro [51] Int. Cl. F22b37/66 tect the boiler tubes from direct impingement of [58] Field ofSearch 110/98; 122/6 R, 6 A, 235 A burner flames which tend to generateand accelerate their premature deterioration. The shielding wall of [56] References Cited tile is free-floating with the expansion andcontraction UNITED STATES PATENTS of the boiler tubes, whose load andtemperature varial 738 283 l2/l929 Carlson 110,98 tion in the burnerregion of the furnace area normally 1 775 4 4 22 results in cracking anddecay Of a fiXd continuous 1:955:7o0 4/1934 Snow 122/6 Shielding Wallmaterial as Currently practiced- 2,086,940 7/1937 Kuhner et al... 122/62,705,476 4/1955 Hardgrove 122/6 23 Clams 10 D'awmg Flgures l8 I8A l 2882 8O 82 8O 28 2 8O PATENTEL wave- 3.850.146

SHEET 10F 2 PATENIEL, HUYZS I974 sum 2 BF 2 FIGS FIG. IO

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FlG. 9

REFERENCE TO PRIOR APPLICATION This application is a division of ourearlier copending application Ser. No. 323,872 filed Jan. 15, 1973,bearing the same title, and the benefit of that filing date is claimed.

BACKGROUND OF THE INVENTION The invention pertains to a heat shieldingwall tile and system for securing such tile in a free-floatingrelationship to boiler tubes in a boiler tube furnace which has beenconverted from coal firing to oil firing burners. Most utility boilertube furnace structures were originally designed for and operated over along period of time with coal-fired burners. Because of the distinctivenature of coal firing, the character and distribution of its flame andcombustion gases, the relatively moderate volumes of excess air utilizedby these burners, the design and organization of the lower regions andthe upper superheat andreheat regions of the boiler tubes, such utilityfurnaces developed superheat temperatures and pressures adequate to meetspecified output requirements. However, today, in view of the ecologicaland environmental need to reduce air pollution as an important if not avital operating factor, utility companies have been gradually convertingtheir coal-fired burners to oil-fired burners. Such conversions haveunfortunately also been attended by a consequent reduction in thenecessary specified elevated temperatures in the superheat regions ofthe boiler unless substantial additional excess air is provided to theoil-fired burners. As a result, operating costs of such boiler tubefurnaces have increased markedly due to accelerated corrosion of theboiler tubes and the quantity of input oil fuel required in comparisonwith previously used lower cost coal. More frequent down-time andinspections have also occurred, adding to the cost factor.

ln evaluating the problem of such conversion to oilfiring burners, itwas found that spray coating the lower regions ofthe boiler tubes with awall ofa suitable insulating shielding ceramic material, operating as aninsulating wall while still transmitting a required amount of heat tothe boiler tubes in such lower region; caused a deflection upwardly intothe superheat and reheat regions of the boiler of the combustion gasessufficient to maintain the required elevated temperatures in the latterregions. But the difficulty with such a continuous sprayed wall coatingupon the heat impinging surfaces of the boiler tubes was an expectedcracking, separation and decay of such coating material because of thevariation in temperatures in various regions of the coated tubes due toload variations and expansion and contraction characteristics, whethersuch coating material was anchored by mechanical means to the boilertubes or not so anchored. The load variation in the impingement area ofthe oil-fired flameand combustion gases resulted directly in thermalvariations which occasioned the destructive cracking, separation anddecay of the continuous sprayed-on wall coating material. Once crackingand separation were initiated, the wall crumbled and decayed withconsequent loss of shielding to the boiler tubes in their lower regions,,a lower temperature in the superheat and reheat regions of the boiler,an increased cost factor, and more frequent shut-down for inspection andrepair. The primary difficulty, as observed, appeared to be thevariation in thermal expansion and contraction of the-boiler tubes.

BRIEF GENERAL DESCRIPTION OF THE INVENTION The invention hereindisclosed provides for a shielding wall of discrete ceramic tiles whichmoves and floats relatively freely with the boiler tubes and thus avoidsthe primary difficulties occasioned by the expansion and contractionfactors of the tubes in continuous substantially solid wall surfacing.Individual tiles of a suitable high temperature resistant ceramicmaterial are shaped and designed to dovetail with adjacent lateral,superior and inferior tiles to form a shielding wall of relativeinsulation for the lower regions of the boiler tubes against impingingoil-fired flames and combustion gases. The lowest course of such tilesis supported upon the metallic angle or clips permanently secured to twoor more adjacent boiler tubes, and a plurality of horizontal courses ofthese tiles are laid against the tubes and secured thereto byfree-floating retaining members that hold the tiles to and against theboiler tubes by means of double or duplex bar devices removably securedto and between vertically spaced apart tile supporting angles ormetallic clips fixedly attached to the boiler tubes, as above, whileallowing the tubes to expand and contract without disturbing therelationship of the courses of tile resting freely against the tubes. Asecond superior bank of such tiles can be secured above the first bankand separated slightly therefrom by a second course of permanentlyattached clip members supporting the courses of tile forming such secondbank. The horizontal gap between the two banks of tiles is filled with aheat insulating type of material such as Kaowool, a readily installedand removable material adapted to shield the boiler tubes in the area ofthe gap. Where required or desired, third, fourth and additionalsuperior banks of the ceramic tile can be applied to the water wallboiler tubes until the lower region of the boiler tube furnace has beensufficiently shielded to obtain the required temperature distributionfrom the lower region to the upper superheat region of the boiler unit.

PURPOSES AND OBJECTS OF THE INVENTION It is therefore an object of theinvention to provide a relatively free-floating wall of ceramic tilesecured to boiler tubes in an oil-fired boiler tube furnace. Anotherobject is the provision of vertically arranged files of the ceramic tilesupported upon clip members permanently secured to the boiler tubes. Afurther object is to provide free-floating tile retaining meansanchoring superior courses of the tile to double or duplex bar membersremovably secured to and between horizontal rows of the clip members.Yet another object is to provide, where desired or required, a pluralityof banks of such tiles arranged in horizontal courses, the banks beingspaced slightly vertically apart from each other and the horizontal gaptherebetween filled with a suitable readily removable insulating fillingmaterial. Still a further object is to provide a shielding wall ofceramic tile secured to the boiler tubes to form a shielding insulatingwall for the lower regions of the tubes in order to obtain requiredelevated temperatures in the superheat and reheat regions of the boiler.Yet a further object is to provide a shielding wall of insulating tilewhich is free-floating vertically and laterally, the tiles being readilyindividually removable if necessary for replacement without a majorrepair of the wall. Still another object is to provide a free-floatingbank of tiles to protect the boiler tubes from direct impingement ofburner flames and combustion gases, wherein the boiler tubes are incontiguous tangent relationship, or closely adjacent but spaced apartrelationship, or widely or substantially widely spaced apartrelationship. Still a further object is to maintain and improve highboiler output efficiencies in a boiler tube furnace converted fromcoal-tired to oil-fired burners, and if possible to effect fuel costsavings.

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below, taken inconnection with the accompanying drawings, illustrating by way ofexample a preferred form of the invention. Reference is here made to thedrawings annexed hereto and forming an integral part of thisspecification, in which DRAWINGS FIG. 1 is a front elevational view of aportion of a bank of tiles forming a shielding wall in front of closelyadjacent continuous tangent boiler tubes, embodying features utilizingthe inventive system.

FIGS. 2 and 3 are to and bottom perspective views respectively to thetile illustrated in FIG. 1.

FIG. 4 is a horizontal sectional view taken substantially on the line 44of FIG. 5.

FIG. 5 is a side vertical sectional view taken substantially on the line55 of FIG. 6.

FIG. 6 is a horizontal sectional view taken substantially on the line6-6 of FIG. 5.

FIG. 7 is a perspective view showing the free-floating tile retainingclip positioned before insertion'between the two bars of thefree-floating duplex bar member, for the construction illustrated inFIGS. 5 and 6.

FIG. 8 is a perspective view similar to that illustrated in FIG. 7 butshowing the free-floating tile retaining clip engaged with thefree-floating duplex bar member, as in FIG. 5. v

FIG. 9 is a perspective view of the free-floating duplex bar member.

FIG. 10 is a fragmentary enlarged horizontal sectional view. similar toFIG. 4, illustrating the conjunctive relationship of the duplex barmember and the tile supporting clip.

SPECIFIC DESCRIPTION One modern boiler design specifies that the boilertubes be brought into contiguous or tangent parallel contact with eachother to form a solid water wall toward and against which theburner-generated flames and combustion gases are directed. Such boilertubes, of conventional tubular shape, are provided on their outersurfaces with longitudinally extending lateral flanges or ribs,substantially 180 apart, which are welded, or otherwise fixedly secured,to the body of the boiler tube. When these flanged tubes are installed,adjacent abutting edges of the flanges are welded to each other to forma continuous uninterrupted wall of boiler tubes. A modified preferredform of the invention disclosed in our co-pending application Ser. 'No.323.872, of which this application is a division, to accommodate suchwall of boiler tube construction is described below and illustrated inthe drawings. The drawing views correspond to FIGS. 23-30 inclusive ofthe aboveidentified co-pending parent application.

The heat shielding wall 10 comprises one or more banks 12 of ceramictiles 14 arranged in horizontal courses 16 one above the other, toshield the boiler tubes 18 therebehind. Water filled tubes 18, at leastin the lower region of the boiler furnace area, are disposed in verticalclosely adjacent contiguous tangent parallel aligned relationship toform a water wall" against and upon which the combustion gasesdischarged by the burners would normally impinge to heat the watertherewithin to the elevated temperatures required for the generation ofsteam which rises from these lower tube regions into the superheat andreheat regions of the boiler unit. Because the superheat and reheatregions of the boiler tubes are substantially elevated above the burnerportion of the boiler furnace, the rising combustion gases operate toincrease the temperature of the steam to superheat temperatures in theupper regions of the boiler tubes due to the shielding effect of theceramic tile wall 10.

The tiles 14 comprise a heat resistant ceramic fire brick body 19 havinga substantially planar distal front hot face wall surface 20, adjacentlateral side walls 22,22 extending rearwardly from the wall surface 20and having a longitudinally extending rib portion 24 on one wall and acomplementary recess 26 on the opposite lateral wall, an upper slot 28extending transversely of the tile from one side edge to the otherrearwardly of the rib 24 and recess 26, a first distal top surface 30intermediate the side walls 22,22 and extending from the front facingwall 20 to the depending wall 32 defining one side of the slot 28, asecond proximal top surface 34 extending from inner wall 36 of the slot28 to the arcuate edges of the longitudinally extending closely adjacentconcavely curved wall surfaces 38,38 intermediate the side walls 22,22and spaced apart from each other by the proximal medial web surface 40having a longitudinally extending groove or slot 41 substantiallymedially between the arcuate concavely curved wall surfaces 38,38, and afirst distal bottom surface 42 extending from the front facing wall 20to a vertically depending stop wall surface 44, and a second proximalbottom surface 46-extending from the latter wallsurface 44 to the loweredges of the arcuate wall surfaces 38,38 and to the web surface 40 andslot 41 between the lateral walls 22,22, the second bottom surface 46being disposed substantially parallel to and below the adjacent firstbottom surface 42.

The ceramic tile 14 is formed of a fire clay type of material suitablefor use in the furnace region of the boiler unit in which substantialelevated temperatures are achieved, often of the order of more than2,000F. The hot face 20 of the ceramic tile is positioned in a planeforwardly of the boiler tubes 18 against which the tiles are designed torest, to receive the impinging effect of the burner flame and combustiongases. The

arcuate wall surfaces 38,38 have a curvature complementary to thecylindrical configuration of the water tubes 18 so that substantiallyoptimum contact can be made between such tile surfaces and the tubesagainst which they rest.

To support the courses 16 of the tiles in each bank 12 upon the boilertubes and in relatively free-floating relationship thereto, supportangle clips and freefloating tile retaining clips are used to retain theceramic tile 14 adjacent and against the boilertubes 18.

The permanently affixed support clip 60 comprises a plate portion 62having arcuate edges 64,64 spaced apart by a medial portion 66 andintermediate substantially co-planar lateral outer edge portionsadjacent the lateral sides 68,68 of the plate portion 62, and anupstanding tile retaining flange 72 at its distal edge. The

I arcuate edges 64,64 have a curvature complementary to thecross-sectional curvature of the outer surface of the cylindrical boilertubes 18,18 (FIG. 4), to which they are permanently affixed by weldingas at 74,74.

The supporting clips 60 are shown (FIG. 1) positioned in spaced apartsubstantially horizontal alignment so that the first course 16 of tiles14 will rest thereon in a substantially straight row, although a lessregular arrangement and organization may also be adopted. The tiledepending face 44, bottom face 46, the lower region of the arcuate wallsurfaces 38,38, and proximal web 40 and slot 41 define the proximallower flange portion 76 of the tile'positioned inwardly of the retainingflange 72 of clips 60, the arcuate surfaces 38,38 lying substantiallyclosely adjacent or abutting the cylindrical outer wall surface of theadjacent boiler tubes 18,18. The proximal bottom surface 46 of the tile14 rests directly upon the plate portion 62 of the clip 60 (FlG. 5). Theproximal upper flange portion 78 of tile 14 is defined by the transverseslot wall surface 36,

the lateral walls 22,22, the concavely curved proximal wall surfaces38,38, and the portion of proximal web 40 and slot 41 lying in thehorizontal planeof the slot 28.

As shown particularly in FlG. l, in a single course 16, a single tile 14rests medially between adjacent boiler tubes 18,18, allowing portions ofadjacent lateral tiles 14,14 to rest in part upon lateral portions ofthe plate portion 62 ofa single supporting angle clip 60, thusdistributing the weight of one full tile and portions of two adjacentlateral tiles upon a single clip 60. The adjacent tiles of each coursearedisposed in very slightly spaced apart relationship, with the lateralribs 24 and recesses 26 of adjacent tiles dovetailing each other insimilar spaced relationship (FIG. 6).

The boiler tubes 18a comprise the tubes 18 and outer longitudinallyextending flanges or ribs 79 at each side thereof, substantiallyl80apart, which are welded to the tubes 18. When installed, the tuberibs 79 are welded to each other at their abutting edges or surfaces toform a continuous imperforate wall or boiler tubes 18a.

Since tiles 14 are of substantially identical shape and size, superiorcourses of tiles also rest on inferior tile courses in substantiallystraight lines. To support the tiles 14 in horizontal courses andvertical files in a bank l2,'the angle clip 60 is further provided withan intermediate medial notch 256 adjacent plate portions 257,257 betweenthe arcuate edges 64,64, lateral end portions 258,258 each having acorner notch 260 adjacent plate portion 259 which, in complement withthe adjacent corner notch 260 of the next adjacent clip 60, forms anotch substantially equivalent to the medial notch 256, between theboiler tubes 18a,18a where the lateral edges of the clips 60,60 arepresent. The lateral edges of adjacent clips 60,60 are preferably spacedapart to allow for some movement toward each other without contact underthe expansion/contraction movements of the adjacent boiler tubes l8a,l8a(HO. 4).

Freefloating tile retaining clips are used with the tile retainingparallel duplex bar device 272 which comprises a pair of bars 274,274secured together in parallel spaced apart relationship at one end by apin 276 having an intermediate web section 278 and laterally outwardlyextending end portions 280,280 and at the other end by a pair of spacerbars 282,282 secured to and between the bars 274,274 in a plane normalto the axis of the pin 276 and having depending end portions 284,284extending beyond the lower ends of the bars 274,274. As will bedescribed below, the bar device 272 is free-floating in the tilesupporting clip notches 256 and adjacent corner notches 260,260 ofadjacent supporting clips 60.

The free-floating tile retaining clip 80 comprises a distal tileanchoring plate member 82, a stem or post 84 having one end securedsubstantially central of and to the rearward side of the plate member 82and its other end to a proximal retaining member 86. The thickness ordiameter of the stem 84 and the proximal retaining member 86 is such asto pass these components easily and freely between the bars 274,274 ofthe duplex bar device 272, and the length and width of the retainingmember 86 are such as to clear without engagement the outer surfaces ofthe boiler tubes 18,18 next thereto adjacent, while great enough toengage the bars 274,274 when rotated into a plane normal to the axis ofthe bars.

The retaining member 86 is first presented to the duplex bar device 272as illustrated in FIG. 7, the member being aligned with and in the planeof the open space between the bars 274,274 of the bar device 272, theninserted therebetween until the proximal retaining member 86 clears theback side of the device 272. When the distal plate portion 82 is rotated90 so that the member 86 lies in a plane normal to the axis of the bars274,274, the tile retaining clip 80 is engaged for tile retention (FIG.8).

As will be seen more particularly in FIGS. 5 and 6, the tile retainingduplex bar device 272, which is preferably of a length sufficient toaccommodate a plurality of horizontal courses 16 of tiles 14 betweenvertically spaced apart supporting clips 60 provided for each bankoftiles (FIG. 5), is first supported upon a superior supporting tileclip 60 in each notch 256 and adjacent corner notches 260,260, disposedbetween the boiler tubes 18,18, by the outwardly extending lateral endportions 280,280 of cross pin 276 which engage the plate portions257,257 on either side of and adjacent the medial notch 256, or engagethe lateral plate portion 259,259 adjacent the corner notches 260,260 ofadjacent tile supporting clips 60.

Generally, more than one horizontal course of tiles is laid up in abank. Since the dimensions of these tiles are approximately 12 incheshigh by about 3 inches wide, their width depending substantially uponthe center to center relationship of the boiler tubes taken inhorizontal section, several horizontal courses of tiles 14 can besupported upon the clips 60. The length of the bar device generallycorresponds to the height of the bank 12 of tiles 14.

Once the duplex bar devices 272 are supported upon the superior clips60, the tiles 14 are laid up upon the supporting clips in a horizontalcourse, and the freefloating tile retaining clips 80 for each tile arepresented to the bar devices 272 as above described, inserted betweenthe bars 274,274 and rotated for engagement therewith, the distal plateportions 82 being dropped into the transverse slot or groove 28 of thetiles as the post or stem portion 84 rests upon the tile proximal upperwall surface 34. After a full bank 12 of the tiles 14 has been laid upupon the clips 60 and retained by the clips 80 and the duplex bar device272, the next superior bank of tiles is laid up upon the next superiorsupporting clips 60 (FIG. The tile retaining duplex bar devices 272 forthe superior bank are now supported by pins 276 upon the next superiorsupporting clips 60 within the notches 256 and 260,260, and dependtoward and substantially in alignment with the duplex bar devices 272 ofthe inferior laid up bank of tiles. The duplex bar devices 272 now lineup by virtue of the spacer bar portions 284,284 which depend from thelower ends of the bar members 274,274, and these portions pass into thespace between the bar members 274,274 and about each side of the pinmedial web portion 278 at the upper end of the next inferior duplex bardevice 272, to form a continuous aligned engaging duplex bar device forthe free-floating clips 80. Each duplex bar device 272 is free-floatingfor its bank 12 of tiles 14, being suspended by the pin 276 from thenext superior supporting clip 60.

It will of course be recognized that, although the boiler tubes 18 ofthe combination tubes 18a, the latter being the tubes 18 with theirlateral flanges 79, are very closely adjacent each other, they are notin fact touching each other, the space therebetween being filled by theadjacent attached flanges 79,79, so that the boiler tubes 18 areslightly spaced apart from each other to permit some relative expansionand contraction movement ofthe tubes. Conductionof heat through the tubeflanges 79 provides means for more rapid heat transmission and thermalequalization in the water wall, a stabilization factor that reduces therange of expansion and contraction movement.

Alternate Application of the Invention Although the heat shielding walldescribed above was designed and developed for the purpose of'deflectingheat generated by burner produced combustion gases into the uppersuperheat'and reheat'region of the boiler, there are instanceswhere thewall of tiles can be used to protect the lower regions of boiler tubesagainst direct burner generated flame impingement while absorbing theheat of the combustion gases to transmit them by conduction, radiationor convection directly to the lower regions of the boiler tubes wherethat is the desired or required purpose. Because direct flameimpingement upon the boiler tubes, particularly in coilfired furnaces,can result in accelerated deterioration of the boiler tubes, it is mostdesirable to shield such tubes from direct flames. To effect thisresult, the tiles 14 can be made of a silicon carbide composition whichis a very good ceramic heat conductor. Such tiles will absorb heatgenerated by the burners and at the same time protect the boiler tubesfrom direct flame impingement, thereby extending their useful life inthe boiler unit.

The tiles l4 disclosed herein are preferably made of ceramic orequivalent materials according to conventional fire-brick manufacturingpractice. The tile supporting clips 60 are preferably made of sheetstock stainless steel or equivalent alloys such as for example the No.309 alloy, or they may be cast. The tile retaining clips 80 and the tileretaining duplex bar device 272 are preferably made of sheet, or sheetand rod, or bar stock, or cast stainless steel or equivalent alloys,such for example as the NO. -12 alloy. The selection of proper andsuitable materials for the tiles, clips and duplex bar device will ofcourse vary in some measure according to engineering preference andstandards, and in view of particular boiler furnace and tube conditionsand the firing equipment being used therein, such selection being wellwithin the competence of persons skilled in the art and having theforegoing disclosure available to them.

It will be at once observed that the system of this invention, whileproviding a more satisfactory solution to the problems of heatdistribution first above described, also permits a selectivereplacement, removal or repair of damaged tiles without in any wayaffecting adjacent portions of the shielding wall 10 not involved insuch damage. Thus, the costs in labor and materials to repair anydamaged portion of the shielding wall 10 is substantially and materiallyreduced, by comparison with present day practices referred to generallyabove. In

' addition, of course, the advantages of free-floating movement of theshielding wall 10 upon general or 10- calized expansion and contractionof the boiler tubes, varying from region to region in the boiler tubefurnace and from portion to portion in the boiler tube, are of paramountimportance and should contribute substantially to an improvement in thecost factor.

Although a certain particular embodiment of the invention ishereindisclosed for purposes of explanation, further modificationsthereof, after study of this specification, may or will become apparentto those skilled in the art to which the invention pertains. Referenceshould be had to the appended claims in determining the scope of theinvention.

We claim:

1. In a wall of ceramic fire brick or tile to shield at least a portionof a water wall of substantially parallel closely adjacent but spacedapartboiler tubes, secured together to form an impenetrable water wallby lateral rib members affixed to saidboiler tubes and to each other,and extending vertically upwardly in and from the burner region of aboiler tu'be furnace area, from direct impingement 'of burner-producedflames and combustion gases upon the facing exposed surfaces of saidboiler tubes, and to deflect a significant portion of the heat generatedby said flanges and combustion gases into the superheat region of theboiler unit thereabove, the improvement combination comprising at leastone pair of said parallel closely adjacent but spaced apart verticallyextending boiler tubes, a plurality of shielding tiles for said boilertubes, means to support said plurality of shielding tiles insubstantially vertical files adjacent the said facing exposed surfacesof said boiler tubes, said support means being fixedly secured to saidboiler tubes, and free-floating tile retaining means comprising a bardevice manually removably engageable with said support means and afree-floating tile retaining clip manually removably engageable with anupper portion of each said tile in said files and with said bar device,to secure each said tile in shielding relationship to said boiler tubes,each of said tiles comprising a unitary ceramic body having a distalfront face, lateral side walls,

a proximal rear face, and a top wall surface having a transverse slottherein, one of said side walls having a longitudinally extending ribportion and the other of said side walls having a longitudinallyextending recess complementary to said rib portion, said rib portion andrecess being aligned with each other transversely of said body, wherebysaid tiles are relatively free-floating with the expansion andcontraction movements of said boiler tubes, and said rib portions andrecesses of laterally adjacent tiles dovetail with each other when saidtiles are arranged in parallel side-by-side relationship. 2. Thestructural combination defined in claim 1, wherein said means to supportsaid plurality of shielding tiles comprises a plate portion disposed atan angle to the plane of said boiler tubes and fixedly secured to saidboiler tubes, and a tile retaining portion at the distal edge of saidplate portion to engage said tile resting upon said plate portion andretain the same thereon. 3. The structural combination defined in claim2, wherein said plate portion is provided with a proximal edgesubstantially complementary to the facing exposed surfaces of saidboiler tubes, portions of said proximal edge being welded to said boilertube surfaces. 4. The structural combination defined in claim 2, whereinsaid plate and tile retaining portions comprise a unitary angle plate.5. The structural combination defined in claim 3, wherein said boilertubes are cylindrical and have convexly v curved outer facing surfacesextending axially of said tubes, and said plate portion proximal edge isprovided with concavely arcuate portions complementary to said boilertube convexly curved outer facing surfaces. 6. The structuralcombination defined in claim 5, wherein said arcuate edge portions areat least in part welded to said boiler tube surfaces. 7. The structuralcombination defined in claim 5, wherein said plate portion proximal edgeis further provided with a notch in the web portion intermediate saidconcavely arcuate edge portions, and a notch at each corner of saidproximal edge. 8. The structural combination defined in claim 7, whereinsaid tile support means further comprises a plurality of said plateportions arranged in horizontal alignment and secured to a plurality ofpairs of said boiler tubes, said notches at adjacent corners of eachplate portion proximal edge forming a combination notch substantiallyequal in width and depth to said web portion notch. 9. The structuralcombination defined in claim 2, wherein said distal tile retainingportion comprises an upstanding flange.

10. The structural combination defined in claim 1, wherein said tileceramic body top wall surface transverse slot extends from one side wallto the other, said transverse slot being spaced from and extendingsubstantially parallel to said distal front face. 11. The structuralcombination defined in claim 10, wherein said tile body furthercomprises a distal undercut bottom wall surface extending rearwardly toa depending proximal lower flange portion. 12. The structuralcombination defined in claim 10, wherein said proximal rear facecomprises a pair of substantially adjacent longitudinally extendingsubstantially parallel concavely curved wall surfaces, said concavelycurved wall surfaces being spaced apart by a medial longitudinallyextending web portion therebetween, said concavely curved wall surfaceshaving a transverse curvature substantially complementary to theadjacent portion of the outer facing surfaces of said boiler tubes. 13.The structural combination defined in claim 10, wherein said tile bodyfurther comprises a proximal upper flange portion extending rearwardlyof said slot and being lower in height than said top wall surface. 14.The structural combination defined in claim 12, wherein said web portionintermediate said concavely curved wall surfaces is provided with alongitudinal slot extending the length of said proximal rear face. 15.The structural combination defined in claim 8, wherein said bar devicecomprises a pair of parallel bars, a pin securing said parallel bars inspaced apart relationship and fixedly positioned adjacent one end ofsaid parallel bars, said pin having end portions extending laterallyoutwardly from said parallel bars at each side of said bar device, and apair of spacer bars securing said parallel bars in spaced apartrelationship and fixedly positioned at the opposite end of said parallelbars and therebetween. 16. The structural combination defined in claim15, wherein said spacer bars lie in a plane normal to the axis of saidpin, and in spaced apart relationship a distance substantially equal toand slightly greater than the diameter of said pin, said spacer barsextending longitudinally from and beyond the ends of said parallel bars.17. The structural combination defined in claim 16, wherein said pin andsaid spacer bars secure said parallel bars in substantially parallelspaced apart relationship throughout their longitudinal extent. 18. Thestructural combination defined in claim 16, wherein each said bar deviceis longitudinally alignable and removably engageable with substantiallyidentical bar devices upon inter-engagement of the spacer bars of asuperior bar device with the intermediate web portion of the pin betweensaid parallel bars of an inferior bar device. 19. The structuralcombination defined in claim 15, wherein each said bar device isengageable with and supportable from said support means plate portionsby said pin end portions, said parallel bars extending through saidmedial plate portion notch or said combination notch at the proximalcorners of adjacent plate portions.

21. The structural combination defined in claim 20,

wherein said stem and said bar device engaging member each have across-sectional thickness no greater than the free clear distancebetween said bar device parallel bars, said bar device engaging memberhaving a transverse width substantially greater than such free cleardistance between said bar device parallel bars, whereby the proximalportion of said stem and said bar device engaging member are insertablebetween said parallel bars and, upon rotation of said stem and bardevice engaging member, said free-floating tile retaining means isengaged with said parallel bars.

22. The structural combination defined in claim 21, wherein said bardevice engaging member is planar and, when rotated into engagement withsaid parallel bars, lies in a plane substantially normal to the axis ofsaid bar device. 23. The structural combination defined in claim 1,wherein each said tile comprises a unitary ceramic body of siliconcarbide.

1. In a wall of ceramic fire brick or tile to shield at least a portion of a water wall of substantially parallel closely adjacent but spaced apart boiler tubes, secured together to form an impenetrable water wall by lateral rib members affixed to said boiler tubes and to each other, and extending vertically upwardly in and from the burner region of a boiler tube furnace area, from direct impingement of burner-produced flames and combustion gases upon the facing exposed surfaces of said boiler tubes, and to deflect a significant portion of the heat generated by said flames and combustion gases into the superheat region Of the boiler unit thereabove, the improvement combination comprising at least one pair of said parallel closely adjacent but spaced apart vertically extending boiler tubes, a plurality of shielding tiles for said boiler tubes, means to support said plurality of shielding tiles in substantially vertical files adjacent the said facing exposed surfaces of said boiler tubes, said support means being fixedly secured to said boiler tubes, and free-floating tile retaining means comprising a bar device manually removably engageable with said support means and a free-floating tile retaining clip manually removably engageable with an upper portion of each said tile in said files and with said bar device, to secure each said tile in shielding relationship to said boiler tubes, each of said tiles comprising a unitary ceramic body having a distal front face, lateral side walls, a proximal rear face, and a top wall surface having a transverse slot therein, one of said side walls having a longitudinally extending rib portion and the other of said side walls having a longitudinally extending recess complementary to said rib portion, said rib portion and recess being aligned with each other transversely of said body, whereby said tiles are relatively free-floating with the expansion and contraction movements of said boiler tubes, and said rib portions and recesses of laterally adjacent tiles dovetail with each other when said tiles are arranged in parallel side-by-side relationship.
 2. The structural combination defined in claim 1, wherein said means to support said plurality of shielding tiles comprises a plate portion disposed at an angle to the plane of said boiler tubes and fixedly secured to said boiler tubes, and a tile retaining portion at the distal edge of said plate portion to engage said tile resting upon said plate portion and retain the same thereon.
 3. The structural combination defined in claim 2, wherein said plate portion is provided with a proximal edge substantially complementary to the facing exposed surfaces of said boiler tubes, portions of said proximal edge being welded to said boiler tube surfaces.
 4. The structural combination defined in claim 2, wherein said plate and tile retaining portions comprise a unitary angle plate.
 5. The structural combination defined in claim 3, wherein said boiler tubes are cylindrical and have convexly curved outer facing surfaces extending axially of said tubes, and said plate portion proximal edge is provided with concavely arcuate portions complementary to said boiler tube convexly curved outer facing surfaces.
 6. The structural combination defined in claim 5, wherein said arcuate edge portions are at least in part welded to said boiler tube surfaces.
 7. The structural combination defined in claim 5, wherein said plate portion proximal edge is further provided with a notch in the web portion intermediate said concavely arcuate edge portions, and a notch at each corner of said proximal edge.
 8. The structural combination defined in claim 7, wherein said tile support means further comprises a plurality of said plate portions arranged in horizontal alignment and secured to a plurality of pairs of said boiler tubes, said notches at adjacent corners of each plate portion proximal edge forming a combination notch substantially equal in width and depth to said web portion notch.
 9. The structural combination defined in claim 2, wherein said distal tile retaining portion comprises an upstanding flange.
 10. The structural combination defined in claim 1, wherein said tile ceramic body top wall surface transverse slot extends from one side wall to the other, said transverse slot being spaced from and extending substantially parallel to said distal front face.
 11. The structural combination defined in claim 10, wherein said tile body further comprises a distal undercut bottom wall Surface extending rearwardly to a depending proximal lower flange portion.
 12. The structural combination defined in claim 10, wherein said proximal rear face comprises a pair of substantially adjacent longitudinally extending substantially parallel concavely curved wall surfaces, said concavely curved wall surfaces being spaced apart by a medial longitudinally extending web portion therebetween, said concavely curved wall surfaces having a transverse curvature substantially complementary to the adjacent portion of the outer facing surfaces of said boiler tubes.
 13. The structural combination defined in claim 10, wherein said tile body further comprises a proximal upper flange portion extending rearwardly of said slot and being lower in height than said top wall surface.
 14. The structural combination defined in claim 12, wherein said web portion intermediate said concavely curved wall surfaces is provided with a longitudinal slot extending the length of said proximal rear face.
 15. The structural combination defined in claim 8, wherein said bar device comprises a pair of parallel bars, a pin securing said parallel bars in spaced apart relationship and fixedly positioned adjacent one end of said parallel bars, said pin having end portions extending laterally outwardly from said parallel bars at each side of said bar device, and a pair of spacer bars securing said parallel bars in spaced apart relationship and fixedly positioned at the opposite end of said parallel bars and therebetween.
 16. The structural combination defined in claim 15, wherein said spacer bars lie in a plane normal to the axis of said pin, and in spaced apart relationship a distance substantially equal to and slightly greater than the diameter of said pin, said spacer bars extending longitudinally from and beyond the ends of said parallel bars.
 17. The structural combination defined in claim 16, wherein said pin and said spacer bars secure said parallel bars in substantially parallel spaced apart relationship throughout their longitudinal extent.
 18. The structural combination defined in claim 16, wherein each said bar device is longitudinally alignable and removably engageable with substantially identical bar devices upon inter-engagement of the spacer bars of a superior bar device with the intermediate web portion of the pin between said parallel bars of an inferior bar device.
 19. The structural combination defined in claim 15, wherein each said bar device is engageable with and supportable from said support means plate portions by said pin end portions, said parallel bars extending through said medial plate portion notch or said combination notch at the proximal corners of adjacent plate portions.
 20. The structural combination defined in claim 15, wherein said free-floating tile engaging clip comprises a distal member removably engageable with at least one said tile at its upper end, a stem having one end thereof secured to said distal member and extending axially normal to the plane of said distal member, and a bar device engaging member secured to the proximal end of said stem, extending rearwardly from and in the plane of said stem and substantially normal to the plane of said distal member.
 21. The structural combination defined in claim 20, wherein said stem and said bar device engaging member each have a cross-sectional thickness no greater than the free clear distance between said bar device parallel bars, said bar device engaging member having a transverse width substantially greater than such free clear distance between said bar device parallel bars, whereby the proximal portion of said stem and said bar device engaging member are insertable between said parallel bars and, upon rotation of said stem and bar device engaging member, said free-floating tile retaining means is engaged with said parallel bars.
 22. The structural combiNation defined in claim 21, wherein said bar device engaging member is planar and, when rotated into engagement with said parallel bars, lies in a plane substantially normal to the axis of said bar device.
 23. The structural combination defined in claim 1, wherein each said tile comprises a unitary ceramic body of silicon carbide. 